内核解读之内存管理(2)内存管理三级架构之内存结点node

文章目录

    • 0、概述
    • 1、内存节点node
    • 2、NUMA的初始化

0、概述

结合NUMA的架构,Linux抽象出了三级内存管理架构:内存节点node、内存区域zone和物理页框page。

在NUMA模型中,每个CPU都有自己的本地内存节点(memory node),而且还可以通过QPI总线访问其他CPU下挂的内存节点,只是访问本地内存要比访问其他CPU下的内存的速度高许多,一般经过一次QPI要增加30%的访问时延。

内存节点node是为了解决多处理器内存访问竞争的问题,而内存区域zone是为了解决32位系统内核只有1G的虚拟地址空间,无法管理大于1G的物理内存这个问题,zone按照用途划分成几种类型,比如低端内存区,高端内存区,DMA内存区等。

内核解读之内存管理(2)内存管理三级架构之内存结点node_第1张图片

内核内存管理三级架构

1、内存节点node

NUMA结构下, 每个处理器与一个本地内存直接相连, 而不同处理器之间则通过总线进行进一步的连接。linux内核把物理内存按照CPU节点划分为不同的node, 每个node作为某个cpu结点的本地内存, 而作为其他CPU节点的远程内存, 而UMA结构下, 则任务系统中只存在一个内存node, 这样对于UMA结构来说, 内核把内存当成只有一个内存node节点的伪NUMA。因此,NUMA和UMA的管理方式便一致了。

Linux内核中使用数据结构pg_data_t来表示内存节点node,我们把它叫做结点描述符。如常用的ARM架构为UMA架构。对于UMA架构只有一个内存节点,对于NUMA架构有多个内存节点。

在numa.h中有如下定义:

#ifdef CONFIG_NODES_SHIFT
#define NODES_SHIFT     CONFIG_NODES_SHIFT
#else
#define NODES_SHIFT     0
#endif

#define MAX_NUMNODES    (1 << NODES_SHIFT)

CONFIG_NODES_SHIFT是由用户配置的内存节点的数目。可以看到,对于UMA架构,MAX_NUMNODES等于1。

include/linux/mmzone.h:

/*
 * On NUMA machines, each NUMA node would have a pg_data_t to describe
 * it's memory layout. On UMA machines there is a single pglist_data which
 * describes the whole memory.
 *
 * Memory statistics and page replacement data structures are maintained on a
 * per-zone basis.
 */
typedef struct pglist_data {
	/*
	 * node_zones contains just the zones for THIS node. Not all of the
	 * zones may be populated, but it is the full list. It is referenced by
	 * this node's node_zonelists as well as other node's node_zonelists.
	 */
	struct zone node_zones[MAX_NR_ZONES];
    /* node_zones是一个数组,包含节点中各内存区(ZONE_DMA, ZONE_DMA32, ZONE_NORMAL...)的描述符。*/

	/*
	 * node_zonelists contains references to all zones in all nodes.
	 * Generally the first zones will be references to this node's
	 * node_zones.
	 */
	struct zonelist node_zonelists[MAX_ZONELISTS]; /* 指定了节点的备用zone列表 */
   
/*

struct zonelist {
	struct zoneref _zonerefs[MAX_ZONES_PER_ZONELIST + 1];
}

该结构包含了类型为 struct zoneref 的一个备用列表,由于该备用列表必须包括所有结点的所有内存域,因此由 MAX_NUMNODES * MAX_NZ_ZONES 项组成,外加一个用于标记列表结束的空指针。

/* Maximum number of zones on a zonelist */
#define MAX_ZONES_PER_ZONELIST (MAX_NUMNODES * MAX_NR_ZONES)

/*
 * This struct contains information about a zone in a zonelist. It is stored
 * here to avoid dereferences into large structures and lookups of tables
 */
struct zoneref {
	struct zone *zone;	/* Pointer to actual zone */
	int zone_idx;		/* zone_idx(zoneref->zone) */
};

*/
    
    
	int nr_zones; /* number of populated zones in this node */ /*指示了节点中zone的数目*/
#ifdef CONFIG_FLATMEM	/* means !SPARSEMEM */
	struct page *node_mem_map; /* 平铺式内存模式下,物理page数组,linux为每个物理页分配了一个struct page的管理结构体,并形成了一个结构体数组,node_mem_map即为数组的指针;pfn_to_page和page_to_pfn都借助该数组实 */
#ifdef CONFIG_PAGE_EXTENSION
	struct page_ext *node_page_ext;
#endif
#endif
#if defined(CONFIG_MEMORY_HOTPLUG) || defined(CONFIG_DEFERRED_STRUCT_PAGE_INIT)
	/*
	 * Must be held any time you expect node_start_pfn,
	 * node_present_pages, node_spanned_pages or nr_zones to stay constant.
	 * Also synchronizes pgdat->first_deferred_pfn during deferred page
	 * init.
	 *
	 * pgdat_resize_lock() and pgdat_resize_unlock() are provided to
	 * manipulate node_size_lock without checking for CONFIG_MEMORY_HOTPLUG
	 * or CONFIG_DEFERRED_STRUCT_PAGE_INIT.
	 *
	 * Nests above zone->lock and zone->span_seqlock
	 */
	spinlock_t node_size_lock;
#endif
	unsigned long node_start_pfn;   /* 节点第一页帧逻辑编号 */
	unsigned long node_present_pages; /* total number of physical pages */ /* 节点中物理页帧总数目 */
	unsigned long node_spanned_pages; /* total size of physical page
					     range, including holes */   /* 按照平铺计算的节点物理页帧总数目。由于空洞的存在可能不等于node_present_pages,应该是大于等于node_present_pages。*/
	int node_id; /*结点id*/
	wait_queue_head_t kswapd_wait; /* kswapd页换出守护进程使用的等待队列 */
	wait_queue_head_t pfmemalloc_wait;

	/* workqueues for throttling reclaim for different reasons. */
	wait_queue_head_t reclaim_wait[NR_VMSCAN_THROTTLE];

	atomic_t nr_writeback_throttled;/* nr of writeback-throttled tasks */
	unsigned long nr_reclaim_start;	/* nr pages written while throttled
					 * when throttling started. */
#ifdef CONFIG_MEMORY_HOTPLUG
	struct mutex kswapd_lock;
#endif
	struct task_struct *kswapd;	/* Protected by kswapd_lock */ /* 指针指向kswapd内核线程的进程描述符 */
    /* 每个结点都有一个内核进程kswapd,它的作用就是将进程或内核持有的,但是不常用的页交换到磁盘上,以腾出更多可用内存。不信你可以ps看一下。*/
	int kswapd_order; /* 需要释放的区域的长度,以页阶为单位 */
	enum zone_type kswapd_highest_zoneidx;

	int kswapd_failures;		/* Number of 'reclaimed == 0' runs */

#ifdef CONFIG_COMPACTION
	int kcompactd_max_order;
	enum zone_type kcompactd_highest_zoneidx;
	wait_queue_head_t kcompactd_wait;
	struct task_struct *kcompactd;
	bool proactive_compact_trigger;
#endif
	/*
	 * This is a per-node reserve of pages that are not available
	 * to userspace allocations.
	 */
	unsigned long		totalreserve_pages;

    /* 结点page回收相关 */
#ifdef CONFIG_NUMA
	/*
	 * node reclaim becomes active if more unmapped pages exist.
	 */
	unsigned long		min_unmapped_pages;
	unsigned long		min_slab_pages;
#endif /* CONFIG_NUMA */

	/* Write-intensive fields used by page reclaim */
	CACHELINE_PADDING(_pad1_);

#ifdef CONFIG_DEFERRED_STRUCT_PAGE_INIT
	/*
	 * If memory initialisation on large machines is deferred then this
	 * is the first PFN that needs to be initialised.
	 */
	unsigned long first_deferred_pfn;
#endif /* CONFIG_DEFERRED_STRUCT_PAGE_INIT */

#ifdef CONFIG_TRANSPARENT_HUGEPAGE
	struct deferred_split deferred_split_queue;
#endif

#ifdef CONFIG_NUMA_BALANCING
	/* start time in ms of current promote rate limit period */
	unsigned int nbp_rl_start;
	/* number of promote candidate pages at start time of current rate limit period */
	unsigned long nbp_rl_nr_cand;
	/* promote threshold in ms */
	unsigned int nbp_threshold;
	/* start time in ms of current promote threshold adjustment period */
	unsigned int nbp_th_start;
	/*
	 * number of promote candidate pages at stat time of current promote
	 * threshold adjustment period
	 */
	unsigned long nbp_th_nr_cand;
#endif
	/* Fields commonly accessed by the page reclaim scanner */

	/*
	 * NOTE: THIS IS UNUSED IF MEMCG IS ENABLED.
	 *
	 * Use mem_cgroup_lruvec() to look up lruvecs.
	 */
	struct lruvec		__lruvec;

	unsigned long		flags; /* 结点标记 */

#ifdef CONFIG_LRU_GEN
	/* kswap mm walk data */
	struct lru_gen_mm_walk	mm_walk;
#endif

	CACHELINE_PADDING(_pad2_);

	/* Per-node vmstats */
	struct per_cpu_nodestat __percpu *per_cpu_nodestats;
	atomic_long_t		vm_stat[NR_VM_NODE_STAT_ITEMS];
#ifdef CONFIG_NUMA
	struct memory_tier __rcu *memtier;
#endif
} pg_data_t;

在UMA结构的机器中, 只有一个node结点contig_page_data, 此时NODE_DATA直接指向了全局的contig_page_data, 而与node的编号nid无关,其中全局唯一的内存node结点contig_page_data定义在include/linux/mmzone.h:。

#ifndef CONFIG_NUMA

extern struct pglist_data contig_page_data;
static inline struct pglist_data *NODE_DATA(int nid)
{
	return &contig_page_data;
}

#else /* CONFIG_NUMA */

#include 

#endif /* !CONFIG_NUMA */

定义了NUMA时,NUMA和平台相关,截取arm64的定义如下:

arch/arm64/include/asm/mmzone.h:

/* SPDX-License-Identifier: GPL-2.0 */
#ifndef __ASM_MMZONE_H
#define __ASM_MMZONE_H

#ifdef CONFIG_NUMA

#include 

extern struct pglist_data *node_data[];
#define NODE_DATA(nid)		(node_data[(nid)])

#endif /* CONFIG_NUMA */
#endif /* __ASM_MMZONE_H */

定义了一个全局指针数组node_data用于存放系统的所有node,宏NODE_DATA用于取得指定id的node。

定义了一个全局静态位图数组用于存放各种状态下的node:

/*
 * Array of node states.
 */
nodemask_t node_states[NR_NODE_STATES] __read_mostly = {
	[N_POSSIBLE] = NODE_MASK_ALL,
	[N_ONLINE] = { { [0] = 1UL } },
#ifndef CONFIG_NUMA
	[N_NORMAL_MEMORY] = { { [0] = 1UL } },
#ifdef CONFIG_HIGHMEM
	[N_HIGH_MEMORY] = { { [0] = 1UL } },
#endif
	[N_MEMORY] = { { [0] = 1UL } },
	[N_CPU] = { { [0] = 1UL } },
#endif	/* NUMA */
};
/*
 * Bitmasks that are kept for all the nodes.
 */
enum node_states {
	N_POSSIBLE,		/* The node could become online at some point */
	N_ONLINE,		/* The node is online */
	N_NORMAL_MEMORY,	/* The node has regular memory */
#ifdef CONFIG_HIGHMEM
	N_HIGH_MEMORY,		/* The node has regular or high memory */
#else
	N_HIGH_MEMORY = N_NORMAL_MEMORY,
#endif
	N_MEMORY,		/* The node has memory(regular, high, movable) */
	N_CPU,		/* The node has one or more cpus */
	N_GENERIC_INITIATOR,	/* The node has one or more Generic Initiators */
	NR_NODE_STATES
};

N_POSSIBLE是假定所有的node都可能存在。

N_ONLINE标记在线的结点。

N_MEMORY标记有内存的结点。

上面的位图数组里,都假定至少有一个node。

结合状态位图数组,提供了遍历特定状态结点的宏:

如果没有启用NUMA:
相当于只有一个结点,循环一次即结束:

#define for_each_node_state(node, __state) \
	for ( (node) = 0; (node) == 0; (node) = 1)

如果启用了NUMA:

#define for_each_node_state(__node, __state) \
	for_each_node_mask((__node), node_states[__state])

for_each_node_mask就是去遍历状态位图,挨个取出置位的node:

#if MAX_NUMNODES > 1
#define for_each_node_mask(node, mask)				    \
	for ((node) = first_node(mask);				    \
	     (node >= 0) && (node) < MAX_NUMNODES;		    \
	     (node) = next_node((node), (mask)))
#else /* MAX_NUMNODES == 1 */
#define for_each_node_mask(node, mask)                                  \
	for ((node) = 0; (node) < 1 && !nodes_empty(mask); (node)++)
#endif /* MAX_NUMNODES */

for_each_node是遍历N_POSSIBLE位图,就是遍历可能存在的结点,就是根据配置,所有结点都遍历一遍。

for_each_online_node是遍历N_ONLINE位图,就是遍历在线的结点。

#define for_each_node(node)	   for_each_node_state(node, N_POSSIBLE)
#define for_each_online_node(node) for_each_node_state(node, N_ONLINE)

2、NUMA的初始化

--->setup_arch
  --->bootmem_init
    --->arch_numa_init

如果没有启用NUMA,arch_numa_init是个空函数

如果启用了NUMA:

/**
 * arch_numa_init() - Initialize NUMA
 *
 * Try each configured NUMA initialization method until one succeeds. The
 * last fallback is dummy single node config encompassing whole memory.
 */
void __init arch_numa_init(void)
{
	if (!numa_off) {
		if (!acpi_disabled && !numa_init(arch_acpi_numa_init))
			return;
		if (acpi_disabled && !numa_init(of_numa_init))
			return;
	}

	numa_init(dummy_numa_init); // 失败时才走这里,关闭numa
}

在没有开启acpi时,就是从设备树读取node信息,然后进行初始化。

of_numa_init:

1、从设备树解析出每个cpu所属的node_id,初始化node全局位图numa_nodes_parsed。

2、从设备树解析出每段内存所属的node_id,注册到全局静态早期内存管理器memblock。

3、从设备树解析出两两结点间的距离,初始化全局静态node距离表numa_distance。

numa_init会调用of_numa_init,将从设备树读取到的结果初始化全局结点状态位图,比如哪些结点在线,以及每个结点的内存起始PFN。

static int __init numa_init(int (*init_func)(void))
{
	int ret;

	nodes_clear(numa_nodes_parsed);
	nodes_clear(node_possible_map);
	nodes_clear(node_online_map);

	ret = numa_alloc_distance();
	if (ret < 0)
		return ret;

	ret = init_func();
	if (ret < 0)
		goto out_free_distance;

	if (nodes_empty(numa_nodes_parsed)) {
		pr_info("No NUMA configuration found\n");
		ret = -EINVAL;
		goto out_free_distance;
	}

	ret = numa_register_nodes();
	if (ret < 0)
		goto out_free_distance;

	setup_node_to_cpumask_map();

	return 0;
out_free_distance:
	numa_free_distance();
	return ret;
}

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